DavidHumus writes: The much-publicized international rankings of student test scores — PISA — rank the US lower than it ought to be for two reasons: a sampling bias that includes a higher proportion of lower socio-economic classes from the US than are in the general population and a higher proportion of of US students than non-US who are in the lower socio-economic classes.

If one were to rank comparable classes between the US and the rest of the world, US scores would rise to 4th from 14th in reading and to 10th from 25th in math.